Power generating system

ABSTRACT

Provided is a power generator, including a plurality of wind power generators generating electrical power using wind power energy, and variable-speed wind power generators connected between the power generator and an electrical power system. The variable-speed wind power generators equalize an output of the entire power generating system by outputting power for correcting for a drop in output of the power generator.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. application Ser. No.11/884,373, filed Aug. 15, 2007, which is a U.S. National Stage ofPCT/JP2006/302707, filed Feb. 16, 2006 and claims priority from JapaneseApplication Number 2005-041012, filed Feb. 17, 2005, the disclosures ofwhich are hereby incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to power generating systems combiningpower generators that generate electrical power using natural energy andvariable-speed wind power generators, and more particularly, relates toa power generating system outputting equalized electrical power byvirtue of a variable-speed wind power generator outputting power forcorrecting a drop in output of the power generator.

BACKGROUND ART

In a power generator such as a wind power generator or a solar powergenerator using natural energy, since the output is highly influenced byweather conditions, it is difficult to generate power according todemand. In addition, because system voltages or frequencies varydepending on output fluctuations, the level of deployment is limited dueto system operating restrictions.

In order to overcome these problems, recently, as described inPublication of Japanese Patent No. 3352662 (Patent Document 1) and soforth, there has been progress in the development of a hybrid-typedistributed power supply system that realizes high-quality and stablepower supply by combining a power generator using natural energy with anelectrical power storage device such as a secondary battery, and bycontrolling the output fluctuation of the power generator using theelectrical power storage device.

-   Patent Document 1: Publication of Japanese Patent No. 3352662 (pages    2-7, FIG. 1)

DISCLOSURE OF INVENTION

However, since the electrical power storage device mentioned above isexpensive, it is less feasible in terms of cost effectiveness, thusmaking its further deployment difficult.

The present invention has been conceived to solve the above-describedproblems, and an object thereof is to provide a power generating systemcapable of realizing high-quality and stable power supply, without usingexpensive equipment such as an electrical power storage device.

In order to solve the above problems, the present invention employs thefollowing solutions.

A first aspect of the present invention provides a power generatingsystem including at least one power generator generating electricalpower using natural energy; and at least one variable-speed wind powergenerator for outputting power to correct for a drop in output of thepower generator.

According to this configuration, because at least one variable-speedwind power generator is provided and this variable-speed wind powergenerator outputs power to correct for the drop in output of the powergenerator, it is possible to equalize the output of the power generatingsystem.

The power generator may be, for example, a wind power generator, a solarpower generator, and so on. The wind power generator serving as thepower generator may be, for example, a fixed-speed wind power generator,a variable-speed wind power generator, or a combination thereof.

Since the variable-speed wind power generator is relatively low-costcompared to a conventional electrical power storage device, it ispossible to realize equalization of the output of the power generatingsystem, for example, the output power, at low cost.

In the power generating system, a priority order may be stored inadvance in the variable-speed wind power generator, and power outputtingfor correcting for the drop in output of the power generator may beperformed in order from the variable-speed wind power generator havingthe highest priority order.

According to this configuration, because a priority order is stored inadvance in the variable-speed wind power generator, and an outputcontrol for correcting for the drop in output of the power generator isrealized in order from the variable-speed wind power generator havingthe highest priority order, when, for example, correction for the dropin output of the power generator is sufficiently performed by thevariable-speed wind power generator having the highest priority, thevariable-speed wind power generator having the priority lower than thatperforms normal electrical power generation. As a result, it is possibleto reduce the number of variable-speed wind power generators performingoutput control designed to correct for the drop in output, thus allowingefficient output equalization of the power generating system to beachieved.

In the power generating system, the priority order may be assigned to behigher for the variable-speed wind power generator installed in alocation with more stable wind conditions.

According to this configuration, because the priority order is assignedto be higher for the variable-speed wind power generator installed in alocation with more stable wind conditions, in other words, for thevariable-speed wind power generator having more stable output, it ispossible to efficiently control the correction for the drop in output ofthe power generator using fewer variable-speed wind power generators.

In the above-described power generating system, the priority order maybe changeable according to weather conditions.

Since the output stability of the variable-speed wind power generatorvaries depending on various weather conditions such as the season or thewind direction, by changing the priority order according to theseweather conditions, output control designed to correct for the drop inoutput of the power generator is always realized in order from thevariable-speed wind power generator having more stable output.Accordingly, it is possible to realize efficient equalization of thepower generating system using fewer variable-speed wind powergenerators.

In the power generating system, the number of variable-speed wind powergenerators may be determined according to an estimated maximum value ofan output fluctuation of the power generator.

Since the variable-speed wind power generators are required to performoutput which can correct for the drop in output of the power generator,the number of variable-speed wind power generators must be determined sothat the total output from the variable-speed wind power generatorsexceeds the output that is required to equalize the estimated maximumvalue of the output fluctuation. In other words, the number ofvariable-speed wind power generators is also determined based on anestimated average output from the variable-speed wind power generator.

A second aspect of the present invention provides a variable-speed windpower generator which is connected between a power generator generatingelectrical power using natural energy and an electrical power systemsupplied with electrical power from the power generator, and whichsupplies electrical power to the electrical power system so as tocorrect for a drop in output of the power generator.

The power generating system and the variable-speed wind power generatoraccording to the present invention provides an advantage in that it ispossible to realize high-quality and stable power supply without usingexpensive equipment such as an electrical power storage device.

Still other objects and advantages of the present invention will becomereadily apparent to those skilled in the art from the following detaileddescription, wherein the preferred embodiments of the invention areshown and described, simply by way of illustration of the best modecontemplated of carrying out the invention. As will be realized, theinvention is capable of other and different embodiments, and its severaldetails are capable of modifications in various obvious respects, allwithout departing from the invention. Accordingly, the drawings anddescription thereof are to be regarded as illustrative in nature, andnot as restrictive.

BRIEF DESCRIPTION OF DRAWINGS

Other characteristics and advantages of the invention will becomeapparent with the aid of the description which follows in conjunctionwith the appended drawings which represent:

FIG. 1 is a diagram showing, in outline, the configuration of a powergenerating system according to a first embodiment of the presentinvention.

FIG. 2 is a waveform diagram for explaining the operation of avariable-speed wind power generator according to the first embodiment ofthe present invention.

FIG. 3 is a waveform diagram for explaining the operation of thevariable-speed wind power generator according to the first embodiment ofthe present invention.

FIG. 4 is a diagram showing, in outline, the configuration of a powergenerating system according to a second embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of a power generating system according to the presentinvention will now be described below with reference to the drawings.

FIG. 1 is a block diagram showing, in outline, the configuration of apower generating system according to a first embodiment of the presentinvention.

As shown in FIG. 1, the power generating system according to thisembodiment includes a power generator 10 having a plurality of windpower generators that generate electrical power using natural energy. Inthis case, each of the wind power generators included in the powergenerator 10 may be fixed-speed wind power generators, variable-speedwind power generators, or a combination thereof.

The power generator 10 is connected to an electrical power system 12 viaan electrical power converter 11. A plurality of variable-speed windpower generators 20 a and 20 b are connected between the power generator10 and the electrical power converter 11. These variable-speed windpower generators 20 a and 20 b output power to correct for a drop in theoutput of the power generator 10 (for example, a drop in output power).The number thereof is determined, for example, according to an estimatedmaximum value of an output fluctuation of the power generator 10.

More specifically, as the estimated maximum value of the outputfluctuation of the power generator 10 becomes larger, the number thereofincreases. This is because, the larger the output fluctuation, thegreater the electrical power needed for correcting for the drop in theoutput thereof, thus requiring variable-speed wind power generators tosupply most of the electrical power thereof. In addition, the numberthereof is determined according to the average power generation level ofthe variable-speed wind power generators. According to this embodiment,an example is given in which two variable-speed wind power generatorsare used.

In this embodiment, the variable-speed wind power generator 20 a isconnected between the power generator 10 and the electrical powerconverter 11, and the variable-speed wind power generator 20 b isconnected between the variable-speed wind power generator 20 a and theelectrical power converter 11. Thus, the variable-speed wind powergenerator 20 a is disposed at the upstream side of electrical current,when viewed from the variable-speed wind power generator 20 b.

According to this embodiment, the variable-speed wind power generator 20a is provided for outputting power to correct for the drop in an outputP0 from the power generator 10. In addition, the variable-speed windpower generator 20 b is provided for further correcting for the drop ina total output P2 of the output P0 from the power generator 10 and anoutput P1 from the variable-speed wind power generator 20 a.

The variable-speed wind power generators 20 a and 20 b are, for example,variable-speed wind power generators with an AC-DC-AC link system, andeach includes a generator 21 that is connected to a rotor of a windmill;an active rectifier 22 for converting three-phase AC power output fromthe generator 21 to DC power and outputting it; a DC link 23 forsmoothing the DC power output from the active rectifier 22; an inverter24 for converting the DC power output from the DC link 23 to three-phaseAC power and outputting it; and an electrical power converter 25 forsupplying the output of the inverter 24 to the electrical power system12.

The variable-speed wind power generator 20 a also includes a controldevice 26 a for controlling the output based on the output power P0 fromthe power generator 10.

In addition, the variable-speed wind power generator 20 b includes acontrol device 26 b for controlling the output based on the total outputpower P2 of the power generator 10 and the variable-speed wind powergenerator 20 a.

On an electrical power line 50 connecting the power generator 10 and theelectrical power system 12 described above, an electrical power detector41 is provided between the power generator 10 and the variable-speedwind power generator 20 a for detecting the output power P0 from thepower generator 10. In addition, on the electrical power line 50connecting the power generator 10 and the electrical power system 12described above, an electrical power detector 42 is provided between thevariable-speed wind power generator 20 a and the variable-speed windpower generator 20 b for detecting the total output power P2 of theoutput power P0 from the power generator 10 and the output power P1 fromthe variable-speed wind power generator 20 a.

The output power P0 detected by the electrical power detector 41 isinput to the control device 26 a of the variable-speed wind powergenerator 20 a. The output power P2 detected by the electrical powerdetector 42 is input to the control device 26 b of the variable-speedwind power generator 20 b.

Next, the operation of the power generating system, having the aboveconfiguration, will be described.

First, each wind power generator provided in the power generator 10generates electrical power by receiving wind, and the generatedelectrical power is output from the power generator 10. The output powerP0 from the power generator 10 is detected by the electrical powerdetector 41 provided on the electrical power line 50. This detectionresult is input to the control device 26 a of the variable-speed windpower generator 20 a.

The control device 26 a calculates a target correcting output power P1′(including both active power and reactive power) for making the outputpower P0 approach a target output power P2 obtained by smoothing thisoutput power P0 and controls the active rectifier 22 and the inverter 24so as to make the output power P1 of the variable-speed wind powergenerator 20 a follow this target correcting output power P1′. Here, theabove-described target output power P1′ can be set as desired. Forexample, it is possible to use an output value obtained by inputting theoutput power P0 into a first-order delay compensating circuit or thelike, or a value obtained by multiplying the maximum generatedelectrical power of the power generator 10 by a predetermined ratio (forexample, 95%).

In addition, for example, when the active rectifier 22 and the inverter24 are constituted by a plurality of switching devices, by performingPWM control of these switching devices, the control device 26 a makesthe output power P1 of the variable-speed wind power generator 20 afollow the target correcting output power P1′.

Specifically, as shown at time t1 in FIG. 2, when the target correctingoutput power P1′ is a, and the output power from the generator 21 of thevariable-speed wind power generator 20 a is P (.alpha.<.beta.), thecontrol device 26 a drops the output power.beta. from the generator 21to .alpha. and outputs it. On the other hand, as shown at time t2 inFIG. 2, when the target correcting output power P1′ is .gamma., and theoutput power from the generator 21 of the variable-speed wind powergenerator 20 a is .beta. (.gamma.>.beta.), the output power .beta. fromthe generator 21 is output unchanged.

As described above, by controlling the output power from thevariable-speed wind power generator 20 a, the drop in electrical powerof the output power P0 from the power generator 10 is corrected withinthe power generating range of the generator 21 of the variable-speedwind power generator 20 a.

The output power, that is corrected for the drop in output in this way,in other words, the total output power P2 of the output power P0 fromthe power generator 10 and the output power P1 from the variable-speedwind power generator 20 a, is detected by the electrical power detector42. This detection result is then input to the control device 26 b ofthe variable-speed wind power generator 20 b.

The control device 26 b calculates a target correcting output power P3′for making the output power P2 approach a target output power Poutobtained by correcting for the drop in output of the output power P2 andcontrols the active rectifier 22 and the inverter 24 so as to make anoutput power P3 of variable-speed wind power generator 20 b follow thistarget correcting output power P3′. For example, when the activerectifier 22 and the inverter 24 are constituted of a plurality ofswitching devices, by performing PWM control of these switching devices,the output power of the variable-speed wind power generator 20 b is madeto follow by the target correcting output power P3′.

As a result, in FIG. 2, when the variable-speed wind power generator 20a does not correct for the drop in output sufficiently (for example, thetime t2 in FIG. 2), the electrical power deficit (for example,.gamma.-.beta.) is supplied by the variable-speed wind power generator20 b.

By doing so, the output power P0 from the power generator is correctedby an amount equal to the drop in output by the variable-speed windpower generators 20 a and 20 b. Thus, a equalized output power Pout issupplied to the electrical power system 12 via the electrical powerconverter 11.

As described above, with the power generating system according to thisembodiment, since the relatively low-cost variable-speed wind powergenerators 20 a and 20 b correct for the drop in the output power of thepower generator 10, it is possible to supply high-quality and stableelectrical power at low cost to the electrical power system 12, withoutusing an expensive electrical power storage device and so forth.

As shown in FIG. 2, in the power generating system described above, whenthe variable-speed wind power generator 20 a is capable of substantiallycorrecting for the drop in output of the generator 20 a, the outputcorrection can be realized in the following way.

First, the plurality of variable-speed wind power generators 20 a and 20b provided for correcting for the drop in output are divided into thevariable-speed wind power generator 20 a for mainly correcting for thedrop in output, and the auxiliary variable-speed wind power generator 20b for assisting the variable-speed wind power generator 20 a.

The auxiliary variable-speed wind power generator 20 b basicallyperforms normal operation by reducing the output power. In other words,instead of normal operation where the output power generated by thegenerator 21 of the variable-speed wind power generator 20 b is directlyelectrically converted and supplied, the output power generated by thegenerator 21 is subjected to a partial load operation by a certainamount (for example, 70%), and the partial-load output power is outputto the electrical power line 50.

For example, as shown in FIG. 3, when Pmax is defined as an electricalpower value in a case where the output power of the generator 21 isoutput without being subjected to the partial load operation, Pref,obtained by subjecting this output power Pmax to the partial loadoperation with a predetermined ratio, is defined as the output power P3in normal operation. Then, as shown at time t2 and so forth in FIG. 2,when equalization of the power generator 10 cannot be sufficientlyachieved due to the insufficient output power from the variable-speedwind power generator 20 a, control is performed so as to output anelectrical power deficit obtained by further adding this output power tothe normal output power P3. Accordingly, it is possible to performelectrical power generation even in the variable-speed wind powergenerators provided for correcting for the drop in output power of thepower generator, and it is thus possible to supply a larger amount ofstable electrical power to the electrical power system 12 as the outputof the power generating system.

In the above-described embodiment, when the generated electrical powerP0 from the power generator 10 considerably exceeds the target outputpower P0′, by employing partial-load outputting in the variable-speedwind power generator 20 a by an amount of electrical power equal to theexcess output power, it is possible to make the total output P2 of thepower generator 10 and the variable-speed wind power generator 20 aapproach the target output power P0′.

Next, a second embodiment of the present invention will be describedwith reference to FIG. 4.

A power generating system of this embodiment differs from the powergenerating system according to the first embodiment in that a centralmanagement device 60 is provided for centrally controlling each of thevariable-speed wind power generators 20 a and 20 b, and eachvariable-speed wind power generator 20 a and 20 b controls the outputbased on commands from the central management device 60.

In the power generating system of this embodiment, a description of thefeatures common to the first embodiment is omitted, and only differencesfrom the first embodiment will be described below.

The output power P0 from the power generator 10 is input to the centralmanagement device 60 from the electrical power detector 41, and outputpowers P4 and P5 from the generators 21 provided in the variable-speedwind power generators 20 a and 20 b are input to the central managementdevice 60.

The central management device 60 calculates a target output power forcorrecting for the drop in output of the output power P0 from the powergenerator 10. Based on this target output power and the output powers P4and P5 from the generators 21 of the variable-speed wind powergenerators 20 a and 20 b, the central management device 60 determinesindividual target output powers P4′ and P5′ of the variable-speed windpower generators 20 a and 20 b, respectively.

Specifically, a priority order of the variable-speed wind powergenerators 20 a and 20 b is set in advance in the central managementdevice 60, and the individual target output powers are determined inorder from the higher priority. At this time, when the variable-speedwind power generator having the highest priority is capable ofoutputting the target output power, the target output power is output tothe highest priority variable-speed wind power generator as theindividual target output power, and a command for normal operation isissued to the variable-speed wind power generator having the prioritylower than that.

When the individual target output powers P4′ and P5′ are input to thecontrol devices 26 a and 26 b of each variable-speed wind powergenerator 20 a and 20 b from the central management device 60 in thisway, the control devices 26 a and 26 b control the active rectifiers 22and the inverters 24 so as to make their output powers follow theseindividual target output powers P4′ and P5′. Accordingly, the targetoutput power is output as the total output power of the variable-speedwind power generators 20 a and 20 b.

As a result, the drop in output of the power generator 10 is corrected,and equalized stable output power is supplied to the electrical powersystem 12 via the electrical power converter 11 as the output of thepower generating system.

In the power generating system according to the second embodimentdescribed above, the priority order is preferably assigned to be higherfor the variable-speed wind power generator installed at a location withmore stable wind conditions, in other words, the variable-speed windpower generator having more stable output. By assigning priority in thisway, it is possible to equalize the output of the power generatingsystem efficiently using fewer variable-speed wind power generators.

The above priority order can also be changed according to weatherconditions.

The output stability of the variable-speed wind power generators 20 aand 20 b varies depending on various weather conditions such as theseason or the wind direction. Therefore, by changing the priority orderaccording to these weather conditions, outputs designed to equalize theoutput from the power generator are always realized in order from thevariable-speed wind power generator having more stable output.Accordingly, it is possible to correct for the drop in output of thepower generator using fewer variable-speed wind power generators, thusallowing effective equalization of the output.

Although preferred embodiments of the present invention have beendescribed above with reference to the drawings, the actual configurationis not particularly limited to these embodiments. Various modificationsare possible so long as they do not depart from the spirit of thepresent invention.

First, in the above-described embodiment, the power generator 10 isconstituted of wind power generators, but this is just an example; itmay be constituted, for example, of a power generator that generateselectrical power using natural energy, such as a solar power generator.

Second, the control devices 26 a and 26 b and the central managementdevice 60 may be formed of an analog circuit having a function forrealizing the above control, or may include a computer system such asthat described below.

The control device 26 a or the like is constituted, for example, of acomputer system including, a CPU (central processing unit), a ROM (ReadOnly Memory), a RAM (Random Access Memory), and so on (not shown in thedrawings). A sequence of processing steps for implementing the variousfunctions described above is stored in the ROM or the like, and the CPUreads out the program into the RAM or the like to execute informationprocessing or calculations, thus realizing the above output control andso forth.

It will be readily seen by one of ordinary skill in the art that thepresent invention fulfills all of the objects set forth above. Afterreading the foregoing specification, one of ordinary skill will be ableto affect various changes, substitutions of equivalents and variousother aspects of the invention as broadly disclosed herein. It istherefore intended that the protection granted hereon be limited only bythe definition contained in the appended claims and equivalents thereof.

1. A power generating system comprising: at least one power generator generating electrical power using natural energy; and at least one variable-speed wind power generator that is controlled to normally generate power under a partial load so as to produce electrical power below a rated output, the power generating system being responsive to a drop in a power output of the at least one power generator so as to correct for a drop in a total output of the at least one power generator and the at least one variable-speed wind power generator, by raising an output on the at least one variable-speed wind power generator.
 2. The power generating system according to claim 1, wherein the number of variable-speed wind power generators is determined according to an estimated maximum value of an output fluctuation of the power generator.
 3. The power generating system according to claim 1, further comprising: an auxiliary variable-speed wind power generator for outputting power to correct for a drop in the output power of said variable-speed wind power generator.
 4. The power generating system according to claim 1, further comprising: an auxiliary variable-speed wind power generator, wherein output power of the auxiliary variable-speed wind power generator is controlled depending on the output power of said variable-speed wind power generator.
 5. The power generating system according to claim 3, wherein the auxiliary variable-speed wind power generator is controlled so as to add output power to the normal output power depending on the drop in output power of the variable-speed wind power generator, when the drop in the output power of the variable-speed wind power generator occurs.
 6. The power generating system according to claim 4, wherein the auxiliary variable-speed wind power generator is controlled so as to add output power to the normal output power depending on the drop in output power of the variable-speed wind power generator, when the drop in the output power of the variable-speed wind power generator occurs. 